1. Field of the Invention
Exemplary embodiments of the present invention relate to a recliner for a vehicle seat, and more particularly, to a recliner for a vehicle seat configured to form protrusion portions at both end portions of a cam sleeve and form groove portions, in which the protrusion portions are movable, on wedge blocks, such that a predetermined gap is continuously maintained between the cam sleeve and a pressing protrusion of each wedge block during operation of the recliner.
2. Description of the Related Art
In general, a vehicle is equipped with a seat back, which is pivotable relative to a seat cushion by forming the seat back as a hinge structure, and a recliner allowing the seat back to be mutually switched from a locked state of being fixed to the seat cushion at a certain angle to an unlocked state of being pivotable relative to the seat cushion. That is, a passenger may adjust an angle of the seat back according to the body form or convenience thereof by operation of the recliner.
Such recliners are classified into a lever type recliner in which, when an operation lever is operated, a recliner is unlocked so that a seat back is pushed by a passenger's back to adjust an angle of the seat back, and a rotary type recliner which adjusts an angle of a seat back by turning an operation knob in the form of a dial.
Among the recliners, the rotary type recliner is disclosed in Japanese Patent Laid-Open Publication No. 2010-253101 (Patent Document 1). FIG. 1 shows an example of a conventional rotary type recliner.
As shown in the drawing, a conventional recliner 10 includes a shaft 11, an external gear bracket 12, an internal gear bracket 13, a socket 14, a bush 15, a plate cover 16, a guide ring 17, and a power transmission unit 20.
The external gear bracket 12 is formed, at a center thereof, with a fitting hole 12a, while being formed, at an inside surface thereof, with an external gear 12b. 
The internal gear bracket 13 is formed, at a center thereof, with a central protrusion 13a protruding therefrom, while being formed, at a circumferential surface thereof, with an internal gear 13b which selectively engages with the external gear 12b. The internal gear 13b has the number of gear teeth less than the number of those of the external gear 12b. 
The socket 14 is formed, at a center thereof, with a coupling hole 14a through which the shaft 11 passes so that the shaft 11 is spline-coupled to the socket 14. The socket 14 is formed, at one side surface thereof, with a socket protrusion 14b protruding therefrom so that the socket protrusion 14b is inserted into the central protrusion 13a of the internal bracket 13. The socket 14 is provided with a spring protrusion 14d protruding in a direction opposite to the socket protrusion 14b such that a wedge spring 23 is seated to the spring protrusion 14d. 
The bush 15 is press-fitted and coupled to the fitting hole 12a of the external gear bracket 12.
The power transmission unit 20 rotates the external gear bracket 12 relative to the internal gear bracket 13. The power transmission unit 20 includes a cam sleeve 22 surrounding a portion of an outer peripheral surface of the central protrusion 13a, a pair of wedge blocks 21 provided between the cam sleeve 22 and the bush 15, and a wedge spring 23 which is fitted and installed between the pair of wedge blocks 21 by bending both ends of the wedge spring 23 so as to press the individual wedge blocks 21 in a direction away from each other.
The cam sleeve 22 has a semicircular shape and is configured such that an inner peripheral surface thereof surrounds a portion of the outer peripheral surface of the central protrusion 13a. 
The pair of wedge blocks 21 is provided and each of the wedge blocks 21 has a wedge shape in which a width is narrowed from one end portion adjacent to each other to the other end portion. The pair of wedge blocks 21 perform a locking function preventing rotation of the external gear bracket 12 in a state in which the angle adjustment of the seat back is completed, and the respective one end portions thereof are spaced to face each other in an eccentric space defined between the outer peripheral surface of the central protrusion 13a of the internal gear bracket 13 and an inner peripheral surface of the bush 15.
The other end portion of each wedge block 21 serves to press an end portion of the cam sleeve 22 during operation of the recliner in order to adjust the angle of the seat back and is provided with a pressing protrusion 21a protruding toward the central protrusion 13a of the internal gear bracket 13.
The plate cover 16 encloses one surface (a front surface in FIG. 1) of the external gear bracket 12 so as to prevent decoupling of the socket 14 and the power transmission unit 20 therefrom.
The guide ring 17 surrounds the external gear bracket 12, the internal gear bracket 13, and an outer peripheral surface of the plate cover 16 so that they are integrally coupled.
As shown in FIG. 2, the pair of wedge blocks 21 is configured such that a uniform gap is each formed between respective pressing protrusions 21a and both end portions of the cam sleeve 22.
During operation of the recliner in this state, when the socket 14 presses and rotates any one wedge block (shown in the left in FIG. 2 for example) of the pair of wedge blocks 21, the left wedge block 21 is decoupled in the eccentric space to be unlocked so that the left wedge block 21 and cam sleeve 22 are rotated while a clearance is maintained between the other wedge block 21 and the cam sleeve 22.
Meanwhile, when operation force is removed in a rotated state of the wedge block 21 and the cam sleeve 22, the gap between the pressing protrusion 21a of the left wedge block 21 and the end portion of the cam sleeve 22 is maintained while the left wedge block 21 pressing the cam sleeve 22 is slightly rotated in a counterclockwise direction by elastic force of the wedge spring 23.
However, when the same centers of the external gear bracket 12 and the internal gear bracket 13 are changed by a deviation, a deviation of an axial distance is present therebetween. For this reason, even when the operation force is released by the deviation of an axial distance, a phenomenon occurs in which no gap between the pressing protrusion 21a of the wedge block 21 and the end portion of the cam sleeve 22 is present in at least one of the pair of wedge blocks 21. As such, since the gap between the pressing protrusion 21a of the wedge block 21 and the end portion of the cam sleeve 22 is not present, actuation force for rotating the cam sleeve 22 is additionally required in addition to actuation force for releasing the wedge blocks 21 from the locked state when the recliner is operated to again adjust the angle of the seat back. Consequently, there is a problem in that overall initial actuation force of the recliner is rapidly increased.
[Patent Document 1] Japanese Patent Laid-Open Publication No. 2010-253101